ASON uses a link management protocol (LMP) to manage transport link resources. The LMP functions are: control channel management, link attribute association, link connectivity validation, link fault management and resource discovery, and so on; these functions, however, do not relate to how to allocate and release channel resources in the link. Some link resource allocation strategies can be applied when designing the ASON system, for example, a low channel number preferential allocation strategy can be used to orderly allocate the channel resources.
In addition, the transport link has a set of standard rate levels in an optical network. A basic signal level is a synchronous transmission module STM-1, and the corresponding rate is 155 Mbit/s. High level digital signal series, such as 622 Mbit/s (STM-4) and 2.5 Gbit/s (STM-16), etc., can be formed by byte interleave synchronous multiplexing the low rate level information module (such as STM-1), where the number of multiplexing is a multiple of 4, for example: STM-4=4×STM-1 and STM-16=4×STM-4, and this method for dividing the rate levels is called cascade method.
However, when allocating and releasing the transport link resources in the cascade method, it results in generation of resource fragments inevitably. A special example will be used to illustrate this case in the following. In a certain case, resources of all 16 channels in one STM-16 link are applied, and then resources of 12 channels in all, i.e., channel 1-3, 5-7, 9-11 and 13-15, in the 16 channel are released. The occupation of the channel resources in the link is shown as FIG. 1; although the number of available idle resources is 12 channels, it cannot satisfy to allocate a relatively smaller STM-4 resource, thus link resource fragments are generated. The existence of the link resources fragments results in a serious consequence of wasting bandwidths, thus it needs to rearrange the channel resources in one link and integrate the scattered channel resource fragments into a complete available resource with a broader bandwidth.